Photosynthesis - LECTURE(2!4!13)

7/27/2019 Photosynthesis - LECTURE(2!4!13)

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PHOTOSYNTHESIS


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THE SUN: MAIN SOURCE OF

ENERGY FOR LIFE ON EARTH


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Almost all plants are photosynthetic autotrophs, as

are some bacteria and protists Autotrophs generate their own organic matter through

photosynthesis

Sunlight energy is transformed to energy stored in the

form of chemical bonds

THE BASICS OF PHOTOSYNTHESIS


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Light Energy Harvested by Plants &

Other Photosynthetic Autotrophs


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Different wavelengths of visible light are seen bythe human eye as different colors.

WHY ARE PLANTS GREEN?

Gamma

raysX-rays UV Infrared

Micro-

waves

Radio

waves

Visible light

Wavelength (nm)


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What color of light is least effective

in driving photosynthesis?

ANS. GREEN


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Sunlight minus absorbedwavelengths or colors

equals the apparent color

of an object.

The feathers of male cardinals

are loaded with carotenoid

pigments. These pigments

absorb some wavelengths of

light and reflect others.


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Why are plants green?

Transmitted light


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WHY ARE PLANTS GREEN?

Plant Cellshave Green

Chloroplasts

The thylakoid

membrane of the

chloroplast isimpregnated with

photosynthetic

pigments (i.e.,chlorophylls,

carotenoids).


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Chloroplasts

absorb light

energy andconvert it to

chemical energy

Light Reflectedlight

Absorbedlight

Transmittedlight Chloroplast

THE COLOR OF LIGHT SEEN IS THE

COLOR NOT ABSORBED


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The location and structure of chloroplasts

LEAF

CHLOROPLAST

StromaGrana


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The location and structure of chloroplasts

LEAF CROSS SECTIONMESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outer

membrane

Innermembrane

Thylakoid

compartmentThylakoidStroma

Granum

StromaGrana


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Chloroplasts: Sites of Photosynthesis

Photosynthesis Occurs in chloroplasts, organelles in certain

plants

All green plant parts have chloroplasts and carryout photosynthesis

The leaves have the most chloroplasts

The green color comes from chlorophyll in the

chloroplasts The pigments absorb light energy


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In most plants, photosynthesis occursprimarily in the leaves, in the chloroplasts

A chloroplast contains:

stroma, a fluid grana, stacks of thylakoids

The thylakoids contain chlorophyll

Chlorophyll is the green pigment that captureslight for photosynthesis

Photosynthesis occurs in chloroplasts


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Chloroplasts contain several pigments

Chloroplast Pigments

Chlorophyll a = absorbs blue-violet and red light

Chlorophyll b = absorbs blue and orange light

Carotenoids = absorbs blue-green light

Figure 7.7


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The Calvin cycle makessugar from carbon

dioxide ATP generated by the light

reactions provides the energyfor sugar synthesis

The NADPH produced by the

light reactions provides the

electrons for the reduction of

carbon dioxide to glucose

Light

Chloroplast

Lightreactions

Calvincycle

NADP

ADP+ P

The light reactions

convert solarenergy to chemicalenergy Produce ATP & NADPH

AN OVERVIEW OF PHOTOSYNTHESIS


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Chlorophyll a & bChl a has a methyl

group

Chl b has a carbonyl

group

Porphyrin ring

delocalized e-

Phytol tail


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Primary

electron acceptor

Photon

Reaction

center

PHOTOSYSTEM

Pigment

molecules

of antenna

Molecular Game of Hot Potato


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Cyclic Photophosphorylation Process for ATP generation associated with

some Photosynthetic Bacteria Reaction Center => 700 nm


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Water-splittingphotosystem NADPH-producingphotosystem

ATPmill

Two types of

photosystems

cooperate in the

light reactions


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Primaryelectron acceptor

Primaryelectron acceptor

Photons

PHOTOSYSTEM I

PHOTOSYSTEM II

Energy forsynthesis of

Noncyclic Photophosphorylation Photosystem II regains electrons by splitting

water, leaving O2 gas as a by-product


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The O2 liberated by photosynthesis is madefrom the oxygen in water (H+ and e-)

Plants produce O2 gas by splitting H2O


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2 H+ 1/2

Water-splittingphotosystem

Reaction-center

chlorophyll

Light

Primaryelectronacceptor

Energyto make



NADPH-producingphotosystem

Light

NADP

1

2

3

How the Light Reactions Generate ATP and NADPH


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In the light reactions, there is a flow ofelectrons from____ molecules to ____,

which is reduced to ____, the source of

electron for sugar synthesis in the ____

cycle.

ANS. Water, NADP+, NADPH, Calvin


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Two connected photosystems collect

photons of light and transfer the energy to

chlorophyll electrons

The excited electrons are passed from the

primary electron acceptor to electron

transport chains Their energy ends up in ATP and NADPH

In the light reactions, electron transport

chains generate ATP, NADPH, & O2

Ch i i ATP


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The electron transport chains are arranged

with the photosystems in the thylakoid

membranes and pump H+ through that

membrane The flow of H+ back through the membrane is

harnessed by ATP synthase to make ATP

In the stroma, the H+ ions combine with NADP+to form NADPH

Chemiosmosis powers ATP

synthesis in the light reactions


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The production of ATP by chemiosmosis in

photosynthesis

Thylakoidcompartment(high H+)

Thylakoidmembrane

Stroma(low H+)

Light

Antennamolecules

Light

ELECTRON TRANSPORT

CHAIN

PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE


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What is the advantage of the lightreactions producing NADPH and ATP on

the stroma side of the thylakoid

membrane?

ANS. The Calvin cycle, which consumes

the NADPH and ATP, occurs in the

stroma.


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Review: Photosynthesis uses light

energy to make food molecules

Light

Chloroplast

Photosystem IIElectrontransport

chainsPhotosystem I

CALVINCYCLE Stroma

LIGHT REACTIONS CALVIN CYCLE

Cellularrespiration

Cellulose

Starch

Otherorganiccompounds

A summary of

the chemical

processes ofphotosynthesis
http://www.flickr.com/photos/ghonet/27421952/


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It's not that

easy bein'

green but itis essential for

life on earth!
http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/

Photosynthesis - LECTURE(2!4!13)

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